This bug was originally marked as duplicate of bug 185666, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.
Build: NetBeans IDE Dev (Build nbms-and-javadoc-5216-on-100521)
VM: Java HotSpot(TM) Server VM, 16.3-b01, Java(TM) SE Runtime Environment, 1.6.0_20-b02
OS: Linux
User Comments:
akochnev: Trying to expand databases node in Services
Stacktrace:
java.lang.IllegalArgumentException: Original Node from map {position=101, iconResource=org/netbeans/modules/db/resources/database.gif, name=Databases, original=null, displayName=Databases, instanceCreate=org.openide.nodes.LazyNode@1af24e2[Name=Databases, displayName=Databases]} is null
at org.openide.nodes.LazyNode.switchToOriginal(LazyNode.java:85)
at org.openide.nodes.LazyNode$SwitchChildren.addNotify(LazyNode.java:107)
at org.openide.nodes.Children.callAddNotify(Children.java:554)
at org.openide.nodes.EntrySupport$Default.getArray(EntrySupport.java:758)
at org.openide.nodes.EntrySupport$Default.getNodes(EntrySupport.java:169)
at org.openide.nodes.EntrySupport$Default.getNodes(EntrySupport.java:225)

Look at the exception report's messages.log file. There are some exceptions from the db.RootNode creation associated with access to keystore:
INFO [org.netbeans.core.startup.layers.BinaryFS]: value = org.netbeans.modules.db.explorer.node.RootNode.instance from UI/Runtime/org-netbeans-modules-db-explorer-node-RootNode-instance.instance
org.netbeans.modules.keyring.kde.KWalletProvider$KwalletException: error while trying to access KWallet, during save
at org.netbeans.modules.keyring.kde.KWalletProvider.save(KWalletProvider.java:96)
at org.netbeans.api.keyring.Keyring.save(Keyring.java:110)
at org.netbeans.modules.db.explorer.DatabaseConnectionConvertor$Handler.startElement(DatabaseConnectionConvertor.java:493)
I guess they are the main reason why the Databases node is not created. Is it wise to store something into keyring, when just creating a node?